A method of producing a processed metal product has been proposed in which a metal article the surface of which is partly covered with a mask is subjected to etching treatment to remove a surface layer of predetermined parts of the metal article to thereby form a desired pattern for decoration or other purpose.
In such production methods, masking has conventionally been conducted by the known method of applying a coating liquid containing a polymer component such as a vinyl, epoxy, silicone, polyamide, polyethylene, styrene-butadiene copolymer, or gelatin (JP-B-48-2649 and JP-B-49-27024). (The term "JP-B" as used herein means an examined Japanese patent publication.)
However, the above technique has been defective in that a coating film having a uniform thickness is difficult to form, resulting often in uneven etching, and that it is difficult to strip off the mask after etching treatment. Further problems of the above masking technique have been that the coating film formation necessitates a drying step for removing solvent or a curing step, leading to poor production efficiency, and that it is difficult to control adhesion of the coating film to a metal article. If the coating film has too weak adhesion to a metal article, formation of a precise pattern through etching treatment is difficult because permeation of the etchant beneath the mask occurs at the edge of the mask. If the coating film has too strong adhesion, stripping of the mask after etching treatment is difficult.
In view of the above, the present inventors tried masking of a metal article with a commercially available adhesive sheet. This technique, however, was found unpractical because during etching treatment, permeation of the etchant occurred at the edge of the applied adhesive sheet or the adhesive sheet peeled from the metal article.